If I create a Task with a delay, user that is responsible for that task gets an email after blocking period.

How can be defined trigger time for sending delayed task email notifications - same as daily summary notification emails ?
I can not find EMail.DailyTaskDelayed.TriggerTime in system properties of the engine.

You can write your a process start event bean with your custom criteria to run. I wrote a simple sample that starts a process if the time of day is later than the configured input. Of course you have to make it a little smarter for your task...